The present invention relates to rockbolts and more particularly to an assembly for securing a rockbolt within a borehole.
Rockbolts are long bolts, typically between 8 to 12 feet, used to support surfaces, for example, the roof of an underground excavation. The inner end is secured in a borehole in the surface and the outer end engages a faceplate which engages the surface. There are generally two types of rockbolts: untensioned rockbolts which engage the borehole along substantially the length of the bolt supporting the surface by engaging the overlying rock, and tensioned rockbolts which engage the rock at the inner end and at the outer end compress the surrounding rock. In the grid-like pattern in which the bolts are used, tensioned rockbolts create ribs of compressed rock across the surface which act like beams.
Referring to FIG. 1, a prior art tensioned rockbolt assembly 10 is illustrated. The assembly 10 includes a faceplate 12 positioned about the borehole 14 and a rockbolt 16 extending through the plate 12 into the borehole 14. The inner end of the rockbolt 16 engages and actuates an anchor 18 positioned in the borehole 14. While the anchor 18 is illustrated as an expansion nut and bail, other anchors can be utilized, for example, expanded wedges or curable resins. To tension the rockbolt 10, a nut 20 on the outer end of the rockbolt 16 is tightened against a grout bulb 22 configured to seat against the faceplate 12. A good description of prior rockbolts and anchors can be found in Underground Excavations in Rock by E. Hoek and E. T. Brown.
When rockbolts 10 are permanently installed, it is generally desirable to backfill the borehole 14 with grout after the rockbolt 16 is tensioned to protect the rockbolt 16 and anchor 18 from corrosion. To facilitate such, many prior art rockbolts 10 include a tube 24 extending from the grout bulb 22 toward the inner end of the rockbolt 16. A side opening 26 is provided in the grout bulb 22 for injection of pressurized grout (not shown). A grout sealer 30 is provided adjacent the juncture between the grout bulb 22 and nut 20 to reduce the potential for leaking at the juncture and to ensure the grout flows through the tube 24 toward the inner end of the borehole 14. After filling the inner end, the grout flows back along the outside of the tube 24 to fill the remainder of the borehole 14. A check port 28 is often provided in the faceplate 12 to ensure complete fill of the borehole 14.
The present invention provides an improved rockbolt assembly. The assembly generally comprises a rockbolt, an anchor, a hollow tube assembly, a faceplate and a nut. The rockbolt has a threaded free end and a second end associated with the anchor. The hollow tube assembly has open first and second ends and an internally extending threaded portion, configured to engage the rockbolt free end, which is positioned between the ends. A passage, including at least one channel traversing the threaded portion, extends between the ends of the tube assembly. The tube assembly allows installation of a standard rockbolt and also the direct injection of back-fill grout through an easily accessible open tube which does not require internal sealers. The faceplate has an aperture therethrough adapted to be positioned about the borehole and to receive the tube assembly. The nut directly engages the faceplate and the tube assembly such that tightening of the nut about the tube assembly is translated through the rockbolt to cause engagement of the anchor.